The only thing that keeps any of them from walking is the certainty that they will lose their entire fee if they do so.
So far as I know the same applies to their subsequent appearances on BOTS etc, i.e. if they don't appear they are again in breach of contract.
You can see that some of the evictees appear on BOTS through gritted teeth as it were! Can you imagine the likes of Ron Atkinson appearing on BOTS if it wasn't for the fact that they would lose the money if they did not do so!